Sea-island-type composite fiber, and fiber product including sea-island-type composite fiber

ABSTRACT

A fiber is a sea-island-type composite fiber in which the primary constituent component of the sea section is an aromatic polyester, the moisture absorption/desorption parameter ΔMR is at least 2.0%, and a diagram obtained by connecting the center of gravity of the islands positioned on the outermost periphery of the fiber cross-sectional surface with line segments is a regular polygon having the center of gravity as an apex. A polyester fiber having superior quality with no splitting of the fiber surface caused by dispersion of stress generated due to volume expansion of the fibers when absorbing moisture, no dyeing irregularity or fuzzing when used in a woven or knitted fabric, and no reduction in moisture absorption due to hot-water processing.

TECHNICAL FIELD

This disclosure relates to a polyester fiber having hygroscopicity.

BACKGROUND

Polyester fibers typified by polyethylene terephthalate are widely usedin clothing applications and industrial applications because of theircharacteristics such as having excellent mechanical properties, chemicalresistance, and heat resistance, having characteristic texture withtension and stiffness, hardly absorbing moisture and having small changein properties with wet, and having excellent dimensional stability.However, as described above, polyester fibers do not havehygroscopicity, and they have a problem of getting sweaty or stickyparticularly in a high-temperature and high-humidity environment insummer. Thus, a composite fiber with a polymer having hygroscopicity toimpart hygroscopicity to a polyester fiber has been proposed.

For example, Japanese Patent Laid-open Publication No. 2016-69770proposes a sea-island composite fiber having hygroscopicity in whichpolyethylene terephthalate is used as a sea part and a polyether blockamide copolymer is used as an island part.

International Publication No. 2018/012318 proposes a sea-islandcomposite fiber in which hygroscopicity is imparted to a fiber by usinga polymer having hygroscopicity in an island part, and the thickness ofa sea part present in an outermost layer in a transverse section of thefiber is controlled to reduce breaking of the sea part in a hot watertreatment.

In the sea-island composite fibers disclosed in JP '770 and WO '318, thethickness of the sea part and the number of the island parts are definedregarding the arrangement of the island parts in a transverse section ofthe fiber, but when the single fiber fineness is reduced to obtain asoft texture required for clothing applications, stress generated withvolume swelling of the polymer having hygroscopicity in a hot watertreatment cannot disperse, and breaking such as cracks may occur in thefiber surface. Thus, the quality of a woven or knitted fabric or thelike may degrade because of generation of dyeing unevenness, fuzz, andthe like. Further, there is also a problem of elution of the polymerhaving hygroscopicity because of surface breaking of the fiber, whichlowers the hygroscopicity. In addition, in such fibers, the fibersurface may break when the fibers or a textile made of the fibers areworn, which has been a problem in applying the fibers to clothing thatis repeatedly washed such as an inner, clothing that is repeatedlyabraded such as sports clothing and the like.

There is thus a need to address the above problems, in which breaking ofthe fiber surface is dramatically reduced by dispersing the stressgenerated with volume swelling of the fiber at the time of moistureabsorption. It could therefore be helpful to provide a polyester fiberfree from dyeing unevenness, fuzz and the like when formed into a wovenor knitted fabric, has excellent quality, and does not decrease itshygroscopicity because of a hot water treatment or the like.

SUMMARY

We thus provide:

-   -   (1) A sea-island-type composite fiber including an aromatic        polyester as a main constituent component of a sea part, wherein        the fiber has a moisture absorption/release parameter ΔMR of        2.0% or more, and a figure obtained by connecting centroids of        island parts disposed on an outermost periphery in a transverse        section of the fiber with line segments is a regular polygon        having the centroids as vertexes.    -   (2) The fiber according to (1), wherein the number of the island        parts disposed on the outermost periphery in the transverse        section of the fiber is an odd number.    -   (3) The fiber according to (1) or (2), wherein a ratio C/L of a        radius of curvature C (μm) of a side on a fiber surface side of        an outer periphery of an island part among the island parts        disposed on the outermost periphery in the transverse section of        the fiber to a radius L (μm) of a circumscribed circle including        the island parts disposed on the outermost periphery in the        transverse section of the fiber is 0.50 to 0.90.    -   (4) A fiber product including the sea-island-type composite        fiber according to any one of (1) to (3).

Our composite fibers, in which stress generated with volume swelling ofthe fiber at the time of moisture absorption can be dispersed andbreaking of the fiber surface is reduced, is free from dyeingunevenness, fuzz, and the like when it is formed in a woven or knittedfabric, with which a polyester fiber excellent in quality can beobtained. In addition, since the hygroscopicity does not degrade, thefiber has excellent hygroscopicity, and it can be suitably usedparticularly in clothing applications.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are schematic diagrams of a transverse sectionalstructure of our polyester fiber.

FIGS. 2A, 2B, 2C, and 2D are schematic diagrams of a transversesectional structure of the polyester fiber.

FIG. 3 is a transverse sectional view for explaining a method ofproducing a polyester fiber.

DESCRIPTION OF REFERENCE SIGNS

-   -   1: Sea part    -   2 a, 2 b, 2 c, 2 d, 2 e, 2 f: Island part    -   3 a, 3 b, 3 c: Line segment connecting intersections of any two        straight lines that bisect area of island part (centroids) in        adjacent island parts among island parts disposed on outermost        periphery in transverse section of fiber    -   4: Perfect circle circumscribing two or more of island parts        among island parts disposed on outermost periphery in transverse        section of fiber (circumscribed circle)    -   5: Perfect circle circumscribing one island part at two or more        points (circumscribed circle)    -   6: Minimum thickness of sea part    -   7: Minimum distance between island parts    -   8: Measuring plate    -   9: Distribution plate    -   10: Discharge plate    -   B: Intersection of straight line drawn from intersection of any        two straight lines that bisect area of island part (centroid)        toward any fiber surface and outer periphery of island part    -   Da, db: Intersection of straight line drawn from intersection of        any two straight lines that bisect area of island part        (centroid) toward any adjacent island part and outer periphery        of island part    -   F: Intersection of straight line drawn from intersection of any        two straight lines that bisect area of island part (centroid)        toward any fiber surface and fiber surface    -   Ga, Gb, Gc, Gd, Ge: Intersection of any two straight lines that        bisect area of island part (centroid)

DETAILED DESCRIPTION

Our polyester fiber includes an aromatic polyester as a main component.Having an aromatic polyester as the main component allows the polyesterfiber to have excellent mechanical properties and heat resistance, andthus the polyester fiber has a favorable tactile sensation such astension, stiffness, and dry feeling. Further, since the polyester fiberhas excellent hygroscopicity with a moisture absorption/releaseparameter ΔMR of 2.0% or more, the polyester fiber can obtain a fiberstructure body excellent in wearing comfort as a cooling material.

The fiber having hygroscopicity incorporates water molecules throughphysical adsorption of water molecules to the fiber and/or formation ofan interaction between a functional group in a molecular structure of acomponent constituting the fiber and water molecules. In particular,when the fiber has high hygroscopicity, water molecules are incorporatedinto the fiber, and thus the fiber is swollen in volume. However,aromatic polyesters, which have rigid aromatic rings in their polymerstructures, are hardly deformed, and stress generated with volumeswelling due to moisture absorption cannot disperse, which may causecracks and the like in the fiber surface.

Thus, in the polyester fiber that reduces breaking of the fiber surfacewith volume swelling at the time of moisture absorption, it is importantthat the centroids of the components disposed on the outermost peripheryamong the components disposed inside the fiber in a transverse sectionof the fiber form a regular polygon with line segments connecting thecentroids as vertexes.

The sectional form of the fiber having components disposed inside thefiber in a transverse section of the fiber is preferably a sea-islandcomposite fiber composed of two or more polymers, and the componentsdisposed inside the fiber is island parts. The figure obtained byconnecting the centroids of the components disposed on the outermostperiphery among the components disposed inside the fiber in a transversesection of the fiber, that is, the figure obtained by connecting thecentroids of the island parts disposed on the outermost periphery in atransverse section of the fiber with line segments, is drawn byselecting the centroids such that the line segments do not intersectwith each other except for the centroids as shown in FIG. 1A when thecentroids of the island parts are connected with the line segments. Whenthe centroids of the island parts are connected with line segments asshown in FIG. 1B, the line segments intersect each other at a part otherthan the centroids of the island parts. A figure drawn at this time isnot included in the figure obtained by connecting the centroids of theisland parts disposed on the outermost periphery with line segments. Asshown in FIG. 1C, with respect to an island part 2 f, other island parts(2 a, 2 b, 2 c, 2 d, 2 e) are disposed between the island part 2 f andthe fiber surface. Thus, the island part 2 f is not included in theisland part disposed on the outermost periphery in a transverse sectionof the fiber.

The definition of the regular polygon that is the disposition form ofthe island components as a feature of our fiber will be described.

Regarding the figure obtained by connecting the centroids of the islandparts disposed on the outermost periphery in a transverse section of thefiber with line segments, a figure formed by n line segments is ann-sided polygon, and the length of each line segment is A1, A2, A3 . . .An. When the average value of the lengths of these line segments is Lx,the ratio (A1/Lx, A2/Lx, A3/Lx . . . An/Lx) of the length of each linesegment to the average value Lx is obtained by rounding off the ratio tothe second decimal place, and the ratio is 0.97 to 1.03, it means thatthe figure obtained by connecting the centroids of the island partsdisposed on the outermost periphery in a transverse section of the fiberwith line segments is a regular n-sided polygon.

In the polyester fiber, since the figure obtained by connecting thecentroids of the island parts disposed on the outermost periphery in atransverse section of the fiber with line segments is a regular polygonhaving the centroids as vertexes, vectors of stress generated when thefiber swells in volume because of moisture absorption are diametricallyopposite between adjacent island parts, and the stress is canceledbetween the island parts, which can reduce stress to propagate to thesea part on the fiber surface side. Because the stress to propagate tothe sea part on the fiber surface side is reduced, the fiber surfacehardly breaks, and generation of dyeing unevenness and fuzz can bereduced. On the other hand, when the figure obtained by connecting thecentroids of the island parts disposed on the outermost periphery in atransverse section of the fiber with line segments is not a regularpolygon having the centroids as vertexes, stress generated with volumeswelling at the time of moisture absorption is less likely to disperse,and a point at which stress is concentrated is likely to be generated atthe interface between the island parts and the sea part. For thisreason, the fiber surface may break, dyeing unevenness and fuzz may begenerated, and the quality of a woven fabric or a knitted fabric maydegrade.

As described above, in the polyester fiber, the island componentsdisposed on the outermost periphery are disposed in a regular polygon togreatly improve the problem in the conventional composite fiber having ahygroscopic component, and the number of island parts disposed on theoutermost periphery in a transverse section of the fiber is preferablyan odd number.

Setting the number of island parts disposed on the outermost peripheryto an odd number can reduce concentration of stress generated withvolume swelling due to moisture absorption in a linear shape, candisperse the stress, and can reduce breaking of the fiber surface. Thus,the fiber can reduce generation of dyeing unevenness and fuzz caused bybreaking of the fiber surface and obtain excellent quality when thefiber is formed into a woven or knitted fabric. The number of islandparts disposed on the outermost periphery in a transverse section of thefiber is more preferably an odd number of 9 or less, still morepreferably an odd number of 5 or less, and the minimum number of theisland parts is 3.

In the polyester fiber, the total number of the island parts in atransverse section of the fiber is preferably 15 or less. Setting thetotal number of the island parts in such a range can reduceconcentration of stress generated with volume swelling due to moistureabsorption in a linear shape, can disperse the stress, and can reducebreaking of the fiber surface. Thus, the fiber can reduce generation ofdyeing unevenness and fuzz caused by breaking of the fiber surface andobtain excellent quality when the fiber is formed into a woven orknitted fabric. The total number of the island parts in a transversesection of the fiber is more preferably 10 or less, still morepreferably 6 or less, and the minimum number of the island parts is 3.

In the polyester fiber, a ratio C/L of the radius of curvature C (μm) ofa side on the fiber surface side of the outer periphery of an islandpart disposed on the outermost periphery in a transverse section of thefiber to the radius L (μm) of a circumscribed circle including theisland parts disposed on the outermost periphery in a transverse sectionpf the fiber is preferably 0.50 to 0.90. The circumscribed circleincluding the island parts disposed on the outermost periphery in atransverse section of the fiber is the circle 4 in FIG. 2B, and L is aradius of the circle 4. The radius of curvature C of a side on the fibersurface side of the outer periphery of an island part disposed on theoutermost periphery in a transverse section of the fiber is the radiusof the circle 5 in FIG. 2C obtained by the method described in theExamples.

C/L indicates the sharpness of the curve of the side on the fibersurface side of the outer periphery of the island part disposed on theoutermost periphery in a transverse section of the fiber with respect tothe fiber surface. When C/L is 0.50 or more, stress generated withvolume swelling at the time of moisture absorption is uniformly appliedand dispersed in the sea part, and the fiber surface hardly breaks. C/Lis more preferably 0.55 or more, still more preferably 0.60 or more.When C/L is 0.90 or less, the curve of the side part on the fibersurface side of the outer periphery of the island part disposed on theoutermost periphery in a transverse section of the fiber does not becomelarge, and no corners are formed. Thus, stress generated with volumeswelling at the time of moisture absorption does not concentrate onthese parts, and the fiber surface hardly breaks. C/L is more preferably0.85 or less, still more preferably 0.80 or less. The fact that C/L is1.0 indicates that the bending of the fiber surface is equivalent to thecurve of the side on the fiber surface side of the outer periphery ofthe island part disposed on the outer periphery. A specific example of atransverse section of the fiber includes a core-sheath composite fiberhaving one island part.

In the polyester fiber, the ratio L/R of the radius L (μm) of thecircumscribed circle including all the island parts disposed on theoutermost periphery in a transverse section of the fiber to the fiberradius R (μm) is preferably 0.50 to 0.90.

L/R indicates the thickness of the sea part between the fiber surfaceand the island parts disposed on the outermost periphery in a transversesection of the fiber. When L/R is 0.90 or less, the thickness of the seapart is sufficiently secured with respect to the fiber diameter. Thus,breaking of the sea part due to the stress generated with volumeswelling at the time of moisture absorption can be reduced, generationof dyeing unevenness and fuzz due to breaking of the fiber surfacecaused by breaking of the sea part can be reduced, and the fiber hasexcellent quality when formed into a woven or knitted fabric. Based onthis idea, L/R is more preferably 0.80 or less, still more preferably0.60 or less. When L/R is 0.50 or more, the rigidity with the thicknessof the aromatic polyester disposed in the sea part can be reduced, andstress generated with the volume swelling at the time of moistureabsorption can be reduced.

In the polyester fiber, a ratio S/L of the minimum distance S (μm)between island parts in a transverse section of the fiber to the radiusL (μm) of the circumscribed circle including all the island partsdisposed on the outermost periphery in the transverse section of thefiber is preferably 0.05 to 0.50. The minimum distance between islandparts in a transverse section of the fiber is the line segment 7 in FIG.2D obtained by the method described in Examples.

The minimum distance between the island parts in a transverse section ofthe fiber is the thickness of the sea parts sandwiched between twoadjacent island parts. When S/L is 0.05 or more, stress generated withvolume swelling at the time of moisture absorption is relaxed in the seapart between the island parts, propagation of stress to the sea part isreduced, and breaking of the fiber surface can be reduced. S/L is morepreferably 0.10 or more, still more preferably 0.15 or more. When S/L is0.50 or less, since the distance between island parts is not long, astress relaxation effect by the sea part between the island parts isexhibited, propagation of stress to the sea part on the fiber surfaceside can be reduced, and breaking of the fiber surface can be reduced.Based on this idea, S/L is more preferably 0.40 or less, still morepreferably 0.30 or less.

In the polyester fiber, the minimum thickness of the sea part ispreferably 0.3 μm or more.

The minimum thickness of the sea part is the smallest distance among thedistances between the intersection of a straight line and the outerperiphery of any island part and the intersection of the straight lineand any fiber surface, the straight line being drawn from the centroidof the island part in a transverse section of the fiber toward the fibersurface by the method described in Examples. The minimum thickness isthe length of the line segment 6 in FIG. 2C. When the minimum thicknessof the sea part is 0.3 μm or more, breaking of the sea part due tostress generated with volume swelling at the time of moisture absorptioncan be reduced, generation of dyeing unevenness and fuzz due to breakingof the fiber surface caused by breaking of the sea part can be reduced,and the fiber has excellent quality when formed into a woven or knittedfabric. The minimum thickness is more preferably 1.0 μm or more, stillmore preferably 2.5 μm or more.

The composite ratio of the sea part/island part of the polyester fiberis preferably 50/50 to 90/10 in terms of weight ratio. When theproportion of the sea part is 50 wt % or more, the aromatic polyester ofthe sea part provides excellent mechanical properties and heatresistance, tension, stiffness, and dry feeling, and a fiber structurebody excellent in wearing comfort can be obtained. In addition, breakingof the sea part due to stress generated with volume swelling at the timeof moisture absorption can be reduced, and generation of dyeingunevenness and fuzz due to breaking of the fiber surface caused bybreaking of the sea part is reduced, and the fiber has excellent qualitywhen formed into a woven or knitted fabric. The proportion of the seapart is more preferably 60 wt % or more, still more preferably 70 wt %or more. When the proportion of the sea part of the polyester fiber is90 wt % or less, that is, the proportion of the island part is 10 wt %or more, the rigidity with the thickness of the aromatic polyesterdisposed in the sea part can be reduced, and stress generated withvolume swelling at the time of moisture absorption can be reduced. Basedon this idea, the proportion of the sea part is more preferably 85 wt %or less, still more preferably 80 wt % or less.

The polyester fiber has a moisture absorption/release parameter ΔMR,which is an index of hygroscopicity, of 2.0% or more. ΔMR is adifference in the moisture absorption rate of a fiber at a hightemperature and a high humidity represented by 30° C.×90% RH and at atemperature and a humidity in a standard state represented by 20° C.×65%RH, and the higher ΔMR is, the higher the hygroscopicity of the fiberis. When ΔMR is 2.0% or more, stuffy feeling in clothes is small, andwearing comfort is exhibited. The range of ΔMR is more preferably 2.5%or more, still more preferably 3.0% or more, and particularly preferably4.0% or more. There is no particular upper limit to the range of ΔMR,but the level that can be achieved is about 10%, which is a substantialupper limit. The polyester fiber satisfies the above-described range ofΔMR before and after a hot water treatment such as dyeing.

The aromatic polyester as the main component of the polyester fiber is apolymer composed of a combination of an aromatic dicarboxylic acid andan aliphatic diol, an aliphatic dicarboxylic acid and an aromatic diol,and an aromatic dicarboxylic acid and an aromatic diol. In general, fromthe viewpoint of mechanical properties, heat resistance, andhandleability in production, it is preferable to use an aromaticpolyester composed of a combination of an aromatic dicarboxylic acid andan aliphatic diol.

Specific examples of the aromatic dicarboxylic acid include, but are notlimited to, terephthalic acid, isophthalic acid, phthalic acid, 5-sodiumsulfoisophthalic acid, 5-lithium sulfoisophthalic acid, 5-(tetraalkyl)phosphonium sulfoisophthalic acid, 4,4′-diphenyl dicarboxylic acid, and2,6-naphthalene dicarboxylic acid.

Specific examples of the aliphatic diol include, but are not limited to,ethylene glycol, 1,3-propanediol, 1,4-butanediol, hexanediol,cyclohexanediol, diethylene glycol, hexamethylene glycol, and neopentylglycol.

The method of producing the aromatic polyester is not limited, and thearomatic polyester may be produced by synthesizing monomers by a generalpolycondensation reaction, an addition polymerization reaction, or thelike when raw materials at the time of production are comprehensivelyused as the monomers. The monomers are not limited, and examples thereofinclude petroleum-derived monomers, biomass-derived monomers, andmixtures of the petroleum-derived monomers and the biomass-derivedmonomers.

In addition, the aromatic polyester may be copolymerized or mixed with asecond and third components in addition to the main component withoutdeparting from the desired effect. To have an aromatic polyester as themain constituent component, the copolymerization amount is 10 mol % orless as the monomer amount of the copolymerization component withrespect to the total monomer amount.

In the polyester fiber, the main component of the sea part is anaromatic polyester as described above. However, aromatic polyesterstypically do not have a functional group or the like that forms a stronginteraction with water molecules in the polymer structure. Thus, asexamples of the method of setting the ΔMR of the polyester fiber withinthe above range, adding a hygroscopic compound, disposing a polymerhaving high hygroscopicity (hereinafter, it may be referred to ashygroscopic polymer), treating polymer molecules on the fiber surfacewith ozone or the like to generate a hygroscopic functional group andthe like are given. Of these, it is preferable to dispose a hygroscopicpolymer in the island parts with consideration of obtaining a polyesterfiber having excellent hygroscopicity.

Examples of the hygroscopic polymer suitably disposed in the islandparts of the polyester fiber include polyether esters, polyether amides,polyether ester amides, polyamides, thermoplastic cellulose derivatives,and polyvinylpyrrolidone. Of these, polyether esters, polyether amides,and polyether ester amides containing a polyether as a copolymerizationcomponent are excellent in stability in melt molding, have highhygroscopicity which is intended, and are more preferably used for thepolyester fiber. Further, polyether esters, having excellent affinitywith the aromatic polyester in the sea part and excellent heatresistance of the hygroscopic polymer, have an effect of improving themechanical properties of the resulting sea-island composite fiber, andthey are particularly preferably used. In addition, a polyether estercomposed of polybutylene terephthalate having excellent crystallinityand a polyether is more preferable since elution of the hygroscopicpolymer into hot water can be reduced.

The hygroscopic polymer as described above has high affinity with waterand is easily eluted when brought into contact with water or hot waterin a dyeing treatment. When breaking of the fiber surface occurs becauseof stress generated with volume swelling at the time of moistureabsorption, the hygroscopic polymer in the island parts may come intocontact with hot water and elute off the fiber, leading to degradationof the hygroscopicity of the fiber. Thus, when the hygroscopic polymeris disposed in the island parts, the effect of reducing breaking of thefiber surface because of the composite sectional shape of the polyesterfiber is remarkably exhibited, and a polyester fiber having excellenthygroscopicity is obtained.

In the hygroscopic polymer, the second and third components may becopolymerized or mixed in addition to the main component withoutdeparting from the desired effect, and the copolymerization amount is 10mol % or less as the monomer amount of the copolymerization componentwith respect to the total monomer amount.

As the sectional shape of the polyester fiber, not only a round sectionbut also a wide variety of sectional shapes such as a flat shape, a Yshape, a T shape, a hollow shape, a cross-in-square shape, and a shapelike a hash tag, may be employed.

The polyester fiber may be in any form such as a long fiber (filament)or a short fiber (staple). In a long fiber, a monofilament composed ofone single yarn or a multifilament composed of a plurality of singleyarns may be used. In a short fiber, the cut length and the number ofcrimps are not limited.

The total fineness of the polyester fiber may be appropriately setaccording to the application, but it is preferably 8 dtex or more and150 dtex or less in a long fiber for clothing in practice. The strengthis preferably 1.5 cN/dtex or more for clothing, but the polyester fiberwith a strength of 1.5 cN/dtex or less can also be used without anyproblems by taking measures such as using the fiber together with otherfibers in producing a fabric. The elongation may be appropriately setaccording to the application, but it is preferably 25% or more and 60%or less from the viewpoint of processability in processing into afabric.

The polyester fiber preferably has a single fiber fineness of 6.0 dtexor less. Having a single fiber fineness in such a range can reducerigidity with the thickness of the aromatic polyester disposed in thesea part, and in addition, a fiber structure body having excellentmechanical properties and heat resistance, tension, stiffness, and dryfeeling, and excellent wearing comfort can be obtained. In addition,breaking of the sea part due to stress generated with volume swelling atthe time of moisture absorption can be reduced, and generation of dyeingunevenness and fuzz due to breaking of the fiber surface caused bybreaking of the sea part is reduced, and the fiber has excellent qualitywhen formed into a woven or knitted fabric. The single fiber fineness ismore preferably 4.0 dtex or less, still more preferably 2.0 dtex orless.

The polyester fiber may be obtained by known methods of melt spinningand composite spinning, and examples thereof are as follows. Thespinning method and the composite method are not limited to thoseexemplified herein.

The polyester fiber composed of two or more polymers may be produced bya melt spinning method for the purpose of producing a long fiber, asolution spinning method such as a wet method or a dry-wet method, amelt blowing method and a spunbonding method suitable for obtaining asheet-shaped fiber structure, or the like, and the melt spinning methodis suitable from the viewpoint of enhancing productivity. In the meltspinning method, it is preferable to use a composite spinneret describedlater. When the melt spinning method is used, the spinning temperatureat that time is set to a temperature at which a polymer having ahigh-melting point or a high-viscosity polymer among polymer types to beused exhibits fluidity. The temperature at which the polymer exhibitsfluidity varies depending on the molecular weight, but when thetemperature is set between the melting point of the polymer and themelting point+60° C., the fiber can be stably produced.

A production method by a melt spinning method includes, for example,separately melting a polymer in the sea part and a polymer in the islandpart, measuring and transporting them by using a gear pump, forming acomposite flow to have a specific composite structure as it is by anordinary method, and discharging the composite flow from a spinneret,cooling a thread to room temperature by blowing cooling air with athread cooling device such as a chimney, converging the thread with asupply of oil from an oil supply device, entangling the thread with afluid entangling nozzle device, and passing the thread through a take-uproller and a stretching roller, and then stretching the thread accordingto a ratio of peripheral speeds of the take-up roller and the stretchingroller. Further, the method includes thermally setting the thread with astretching roller and winding the thread with a winder (winding device).There is also a two-step method in which the circumferential speeds ofthe take-up roller and the stretching roller are set to the same speed,and the thread is wound with a winder at the same speed to once form anunstretched yarn, and the yarn is stretched in a separate step.

In the polyester fiber, when the melt viscosity ratio of two or morepolymers used in the sea part and the island part is less than 5.0, acomposite polymer flow can be stably formed, and a fiber having a goodcomposite section can be obtained, which is preferable.

As the composite spinneret used in production of the polyester fiber, acomposite spinneret described in Japanese Patent Laid-open PublicationNo. 2011-208313 is preferably used. The composite spinneret shown inFIG. 3 herein is incorporated into a spinning pack in a state wheremainly three types of members, that is, a measuring plate 8, adistribution plate 9, and a discharge plate 10 are stacked in this orderfrom the top, and the spinneret is used for spinning. FIG. 3 is anexample in which two polymers of A polymer and B polymer are used. Inthe conventional composite spinneret, it is difficult to control theshape of the island part as described above, and it is preferable to usea composite spinneret using a microchannel as exemplified in FIG. 3 .

Of the spinneret members shown in FIG. 3 , the measuring plate 8 has arole of measuring the amount of the polymer per discharge hole and perdistribution hole and flowing the polymer into the distribution plate 9.The distribution plate 9 has a role of controlling the composite sectionand the sectional shape in the single fiber section, and the dischargeplate 10 has a role of compressing and discharging the composite polymerflow formed with the distribution plate 9.

Although not shown in FIG. 3 to avoid complicated illustration of thecomposite spinneret, as for the member stacked above the measuring plate8, a member having a channel may be used in accordance with the spinningmachine and the spinning pack. By designing the measuring plate 8 inaccordance with the existing channel member, the existing spinning packand members of the spinning pack can be used as they are, and there isno need to exclusively use a spinning machine for the spinneret.Further, a plurality of channel plates may be stacked between thechannel and the measuring plate 8 or between the measuring plate 8 andthe distribution plate 9. With this configuration, a flow path can beprovided through which the polymer is efficiently transferred andintroduced into the distribution plate 9 in the spinneret sectionaldirection and the single-fiber sectional direction. The compositepolymer flow discharged from the discharge plate 10 is cooled andsolidified according to the above production method, then an oil agentis applied to the composite polymer flow, and the composite polymer flowis taken up by a roller having a specified peripheral speed, whereby afiber having a desired composite section is obtained.

The polyester fiber can be subjected to post-processing such as falsetwisting or twisting, and it can be handled for weaving and knitting inthe same manner as in n fibers.

The polyester fiber and/or its post-processed yarn may be formed into afiber structure such as a woven fabric, a knitted fabric, a pile fabric,a nonwoven fabric, a spun yarn, or batting according to a known method.The fiber structure composed of the polyester fiber and/or itspost-processed yarn may be any woven or knitted structure. A plainweave, a twill weave, a satin weave, or a weave changed from theseweaves; or warp knitting, weft knitting, circular knitting, lacestitching, knitting or stitching changed from these knitting orstitching or the like can be suitably employed.

Our polyester fiber may be combined with other fibers by union weavingor union knitting in the formation of the fiber structure, or it may becombined with other fibers to form a combined filament yarn and then thecombined filament yarn may be formed into a fiber structure.

The fiber structure body composed of the polyester fiber and/or itspost-processed yarn is excellent in hygroscopicity, and therefore it canbe suitably used in applications requiring comfort and quality. Examplesof the applications include, but are not limited to, general clothingapplications, sports apparel applications, bedding applications,interior applications, and materials applications.

EXAMPLES

Our composite fibers and fiber products will be described in detail withreference to Examples, but this disclosure is not limited to theExamples. Each property value in Examples was obtained by the followingmethod.

A. Melt Viscosity of Polymer

A polymer sample having a moisture content set to 300 ppm or less with avacuum dryer was put into a heating furnace set at the same temperatureas the spinning temperature, melted under a nitrogen atmosphere, andextruded from a capillary at the tip of the heating furnace whilechanging the strain rate stepwise, then the viscosity was measured withCapilograph manufactured by Toyo Seiki Seisaku-sho, Ltd. The measurementwas started after the sample was put into the heating furnace and leftfor 5 minutes, and the value at a shear rate of 1216 sec⁻¹ was taken asthe melt viscosity of the polymer.

B. Melting Point (Tm) of Polymer

Using a differential scanning calorimeter (DSC) model Q2000 manufacturedby TA instruments, 20 mg of the polymer sample was heated from 20° C. to300° C. at a temperature rising rate of 20° C./min, held at 300° C. for5 minutes, then cooled from 300° C. to 20° C. at a temperature fallingrate of 20° C./min, held at a temperature of 20° C. for 1 minute, andfurther heated from 20° C. to 280° C. at a temperature rising rate of20° C./min. A peak top temperature of an endothermic peak then observedwas defined as the melting point. When a plurality of endothermic peakswere observed, the endothermic peak top on the highest temperature sidewas taken as the melting point.

C. Total Fineness

A hank was made by winding the sample yarn 200 times using a wrap reelwith a frame circumference of 1.125 m, the hank was dried with a hot-airdryer (105±2° C.×60 minutes), then the hank was weighed with a balance,and the total fineness was calculated from a value obtained bymultiplying the weight by official moisture regain. The measurement wasperformed four times, and the average was defined as the total fineness.

D. Tensile Strength and Elongation

A measurement was performed under a constant rate of extensionconditions shown in JIS L1013 (chemical fiber filament yarn test method,2010) using “TENSILON” (registered trademark) UCT-100 manufactured byORIENTEC CORPORATION as a measuring instrument. The elongation wascalculated from the elongation at the point showing maximum strength inthe tensile strength-elongation curve. The tensile strength was definedas the value obtained by dividing the maximum strength by the totalfineness. The measurement was performed 10 times, and the average wasdefined as the tensile strength and the elongation.

E. Boiling Water Shrinkage Percentage

A hank was made by winding the fiber sample 20 times using a warp reelwith a frame circumference of 1.125 m, and an initial length L₀ of thesample was determined under a load of 0.09 cN/dtex. Next, the sample wastreated in boiling water under no load for 30 minutes, and thenair-dried. Subsequently, a length L₁ of the sample after the treatmentunder a load of 0.09 cN/dtex was obtained, then calculated with Formula(1):

Boiling water shrinkage percentage (%)=[(L ₀ −L ₁)/L ₀]×100  (1).

F. ΔMR Before Hot Water Treatment

About 1 to 2 g of the fiber sample or a fabric sample was weighed in aweighing bottle, dried at 110° C. for 2 hours, and then the mass wasmeasured, and this mass was defined as w₀. Next, the dried fiber samplewas held at a temperature of 20° C. and a relative humidity of 65% for24 hours, and then the mass was measured, and this mass was defined asw_(65%). Subsequently, the temperature was adjusted to 30° C. and therelative humidity was adjusted to 90%, the fiber sample was held for 24hours, the mass was then measured, and this mass was defined as w_(90%):

MR₁=[(w _(65%) −w ₀)/w ₀]×100  (2)

MR₂=[(w _(90%) −w ₀)/w ₀]×100  (3)

ΔMR=MR₂−MR₁  (4).

At this time, the value calculated from Formulas (2) to (4) was definedas ΔMR.

G. ΔMR after Hot Water Treatment

A tubular knitting was produced by adjusting the fiber sample to have adensity of 50 using a circular knitting machine NCR-BL (pot diameter 3inch and half (8.9 cm), 27 gauge) manufactured by EIKO INDUSTRIAL CO.,LTD. When the regular fineness of the fiber was less than 80 dtex, thefiber was appropriately combined so that the total fineness of the fiberto be fed to the tubular knitting machine was 80 to 160 dtex, and whenthe total fineness was more than 80 dtex, one yarn was fed to thetubular knitting machine, and the tubular knitting was produced byadjusting the fiber sample to have the density of 50 as described above.Next, the obtained tubular knitting was charged into an aqueous solutioncontaining sodium carbonate at 1 g/L and a surfactant SUNMORL BK-80manufactured by NICCA CHEMICAL, CO., LTD, treated for 20 minutes withthe aqueous solution whose temperature was raised to 80° C., and thendried in a hot air dryer at 60° C. for 60 minutes. The tubular knittingafter drying was subjected to a hot water treatment under the conditionsof a bath ratio of 1:100, a treatment temperature of 130° C., and atreatment time of 60 minutes, and then dried in a hot air dryer at 60°C. for 60 minutes to obtain a tubular knitting after the hot watertreatment. For the obtained tubular knitting after the hot watertreatment, ΔMR was calculated according to the description of item F.

H. Radius of Curvature C

The fiber sample was embedded in an embedding agent such as an epoxyresin, and an image was taken at a magnification at which 10 or moresingle fibers can be observed with a scanning electron microscope (SEM)manufactured by HITACHI, Ltd. in a fiber transverse section in adirection perpendicular to the fiber axis. The obtained image wasanalyzed using computer software WinROOF manufactured by MITANICORPORATION to determine the radius of curvature C of a side on thefiber surface side of the outer periphery of the island part disposed onthe outermost periphery in the fiber transverse section.

In obtaining the radius of curvature, first, with reference to FIG. 2C,a straight line was drawn from the centroid G of the island part towardany fiber surface, the length of the line segment BF including theintersection B of the outer periphery of the island part and thestraight line and the intersection F of the fiber surface and thestraight line was measured to the second decimal place, and theintersection B at which the length of the line segment BF has theminimum value was obtained. The radius of a circle that is in contactwith the island part at the intersection B and circumscribes the islandpart, the radius having the minimum value, was obtained up to the thirddecimal place. This operation was performed on all the island partsincluded in one single fiber, and this operation was further performedon three single fibers randomly extracted, and the average value of theobtained radiuses was obtained and rounded off to the second decimalplace. This value was defined as the radius of curvature C (μm).

I. Radius L of Circumscribed Circle

In the same manner as in the item H, an image of a transverse section ofthe fiber was taken by SEM, the image taken with WinROOF was analyzed,the radius of the circumscribed circle including all the island partsdisposed on the outermost periphery in the transverse section of thefiber was measured up to the third decimal place, a simple numberaverage of the results of performing this operation on 10 single fibersrandomly extracted was obtained, then the value obtained by rounding offto the second decimal place was taken as the radius L (μm) of thecircumscribed circle.

J. Fiber Radius R

In the same manner as in the item H, an image of a transverse section ofthe fiber was taken by a SEM, radiuses of single fibers randomlyextracted in the same image from each taken image were measured to thethird decimal place in units of μm, a simple number average of resultsof performing this operation on 10 single fibers randomly extracted wasobtained, then a value obtained by rounding off to the second decimalplace was taken as the fiber radius R (μm). When the transverse sectionof the fiber in a direction perpendicular to the fiber axis was not aperfect circle, the area thereof was measured, and a value obtained byconverting it into a circle was employed.

K. Minimum Distance S Between Island Parts

In the same manner as in the item H, an image of a transverse section ofthe fiber was taken by SEM, and the image taken with WinROOF wasanalyzed to determine the minimum distance S between island parts in thetransverse section of the fiber.

In obtaining the minimum distance between island parts, with referenceto FIG. 2D, for two adjacent island parts 2 a and 2 b, a straight linewas drawn from the centroid Ga of the island part 2 a toward the islandpart 2 b, the intersections of the straight line and the outer peripheryof each island part were defined as Da and db, and the minimum value ofthe length of this line segment Da-db was measured up to the thirddecimal place. This operation was performed on two adjacent island partsat 10 points randomly extracted from island parts included in one singlefiber. When the number of line segments Da-db formed between twoadjacent island parts was less than 10, the minimum value of the linesegments Da-db was measured in all the island parts included in onesingle fiber. This operation was performed on three single fibersrandomly extracted, an average value of lengths of the obtained linesegments Da-db was obtained, and a value obtained by rounding theaverage value off to the second decimal place was taken as the minimumdistance S (μm) between island parts.

L. Minimum Thickness of Sea Part

In the same manner as in the method of obtaining the length of the linesegment BF described in the item H, with reference to FIG. 2C, astraight line was drawn from the centroid Ga of the island part towardany fiber surface, the length of the line segment BF including theintersection B of the outer periphery of the island part and thestraight line and the intersection F of the fiber surface and thestraight line was measured to the second decimal place, and theintersection B at which the length of the line segment BF has theminimum value was obtained. This operation was performed on all theisland parts included in one single fiber, and this operation wasfurther performed on three single fibers randomly extracted, and theaverage value of the obtained line segments BF was obtained and roundedoff to the first decimal place. This value was defined as the minimumthickness (μm) of the sea part.

M. Number of Breaks of Sea Part

A tubular knitting produced by the method described in the item G andsubjected to the hot water treatment was vapor-deposited with aplatinum-palladium alloy and observed at a magnification of 1,000 usingscanning electron microscope (SEM) S-4000 manufactured by HITACHI, Ltd.,and micrographs of 10 fields were randomly taken. In the obtained 10photographs, the fiber surface constituting the tubular knitting wasobserved, and the points where the sea part was broken were counted.When the number of breaks of the sea part was 10 or less, it wasregarded as pass.

N. Dyeing Unevenness

A tubular knitting was produced by the method described in the item G,and the obtained tubular knitting was charged into an aqueous solutioncontaining sodium carbonate at 1 g/L and a surfactant SUNMORL BK-80manufactured by NICCA CHEMICAL, CO., LTD, treated for 20 minutes withthe aqueous solution whose temperature was raised to 80° C., and thendried in a hot air dryer at 60° C. for 60 minutes. Next, the tubularknitting was subjected to dry heat setting at 160° C. for 2 minutes. Thetubular knitting after the dry heat setting was charged into a dyeingsolution in which 1.3 wt % of Kayalon Polyester Blue UT-YA manufacturedby NIPPON KAYAKU, Co., Ltd. was added as a disperse dye to adjust the pHto 5.0, or into a dyeing solution in which 1.0 wt % of Kayacryl Blue2RL-ED manufactured by NIPPON KAYAKU, Co., Ltd. was added as a cationicdye to adjust the pH to 4.0, and dyed under the conditions of a bathratio of 1:100, a dyeing temperature of 130° C., and a dyeing time of 60minutes.

Using the tubular knitting after dyeing as a sample, the L value wasmeasured three times per sample using a spectrophotometer CM-3700dmanufactured by Minolta Co., Ltd. with a D65 light source and a viewingangle of 10° under an optical condition of SCE (specular componentexcluded), and the average value thereof was rounded off to the firstdecimal place to obtain the L value of the sample. This operation wasperformed on 10 samples randomly extracted, and the variation rate wasobtained from the average value and standard deviation of the L valuesof 10 samples. When the variation rate of the L value of the 10 sampleswas 5.0% or less, it was determined that there was no dyeing unevenness.

O. Fuzz Number

Using a multipoint fuzz counting apparatus (MFC-120 manufactured byTORAY ENGINEERING Co., Ltd.), the fiber sample was run at 600 m/min andmeasured for 10,000 m, and the fuzz number displayed on the apparatuswas counted. A warping reed (made of stainless steel, with an intervalof 1 mm between reeds) was provided before the measurement point, andthe fiber was passed therethrough. This measurement was repeated 10times, the average value at 10,000 m was taken as the fuzz number, andwhen the fuzz number was 10/10,000 m or less, it was regarded as pass.

P. Water-Absorbing and Quick-Drying Property

A tubular knitting produced by the method described in the item G andsubjected to the hot water treatment was held at a temperature of 20° C.and a relative humidity of 65% for 24 hours, and then the mass thereofwas measured and taken as w_(a). Next, 0.3 ml of water was dripped tothe center of the sample, and the mass was measured. This mass wasdefined as w_(0min). The moment when water was dripped to the sample wasdefined as 0 minutes, the mass of the sample was measured at intervalsof 5 minutes, and the mass was defined as w_(nmin). n minutes representsa freely-selected time at which the mass of the sample was measured,having 5 minutes of intervals such as 5 minutes, 10 minutes, and 15minutes. The moisture residual ratio WR at the free-selected time wascalculated from Formula (5):

WR=[(w _(0min) −w _(nmin))/(w _(0min) −w _(a))]×100  (5).

When the time at which the moisture residual ratio WR calculated fromFormula (5) was less than 30% was 60 minutes or less, it was determinedthat the sample has water-absorbing and quick-drying properties.

Q. Maintenance of Hygroscopicity Before and After Hot Water Treatment

Change in hygroscopicity of the fiber before and after the hot watertreatment was evaluated with a difference in ΔMR obtained by subtractingΔMR before the hot water treatment calculated in the item F from ΔMRafter the hot water treatment calculated in the item G. When the changein ΔMR was 2.0% or less, it was considered that the hygroscopicity ofthe fiber was maintained before and after the hot water treatment.

Example 1

Polyethylene terephthalate (melt viscosity: 120 Pa·s, melting point:254° C.) was used as the sea part, and polybutylene terephthalate (meltviscosity: 50 Pa·s, melting point: 217° C.) copolymerized with 50 wt %of polyethylene glycol having a number average molecular weight of 8,300g/mol (PEG6000S manufactured by Sanyo Chemical Industries, Ltd.) wasused as the island part. The polymers for the sea part and the islandpart were separately melted at a spinning temperature of 285° C., andthen weighed such that the sea-island ratio was 80:20 in terms of weightratio. The polymers were allowed to flow into a spinning packincorporating the composite spinneret shown in FIG. 3 , and the inflowpolymers were discharged from discharge holes (hole diameter: 0.30 mm,number of holes: 36 holes) to have a sea-island composite form in whichthe number of island parts disposed on the outermost periphery was 3,and the total number of island parts was 3. The discharged compositepolymer flow was cooled and solidified with a cooling device, suppliedwith a water-containing oil agent from an oil supply device, and thenwound up at a peripheral speed of a take-up roller as a first roller of2,000 m/min, a peripheral speed of a stretching roller as a secondroller of 2,000 m/min, and a winding speed of a winder of 2,000 m/min toobtain a polyester fiber of unstretched yarn of 200 dtex and 36filaments. Subsequently, the obtained unstretched yarn was stretched ata first roller temperature of 90° C., a second roller temperature of130° C., and a stretch ratio represented by a ratio between peripheralspeeds of the first roller and the second roller of 2.38 times to obtaina stretched yarn of polyester fiber of 84 dtex and 36 filaments. For atriangle obtained by connecting the centroids of the island partsdisposed on the outermost periphery with line segments in a transversesection of the fiber of the obtained polyester fiber, we confirmed thatthe ratios of the length of each line segment to the average value ofthe lengths of the line segments were 0.97, 1.03, and 0.99, and thefigure obtained by connecting the centroids of the island parts disposedon the outermost periphery with line segments was a regular triangle.The evaluation results of the obtained polyester fiber are shown inTable 1.

Example 2

A stretched yarn of polyester fiber of 84 dtex and 36 filaments wasobtained under the same conditions as in Example 1, except that the seapart was changed to polyethylene terephthalate (melt viscosity: 170Pa·s, melting point: 244° C.) copolymerized with 1.5 mol % of5-sulfoisophthalic acid sodium salt and 1.0 wt % of polyethylene glycolhaving a number average molecular weight of 1,000 g/mol (PEG1000manufactured by Sanyo Chemical Industries, Ltd.). For a triangleobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments in a transverse section of thefiber of the obtained polyester fiber, we confirmed that the ratiosbetween the length of each line segment and the average value of thelengths of the line segments were 0.99, 1.02, and 0.99, and the figureobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments was a regular triangle. Theevaluation results of the obtained polyester fiber are shown in Table 1.

Example 3

A stretched yarn of polyester fiber of 84 dtex and 72 filaments wasobtained under the same conditions as in Example 2 except that thenumber of discharge holes was 72, a polyester fiber of unstretched yarnof 155 dtex and 72 filaments was obtained, and the obtained unstretchedyarn was stretched at a stretch ratio of 1.84 times. For a triangleobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments in a transverse section of thefiber of the obtained polyester fiber, we confirmed that the ratios ofthe length of each line segment to the average value of the lengths ofthe line segments were 0.99, 0.99, and 1.02, and the figure obtained byconnecting the centroids of the island parts disposed on the outermostperiphery with line segments was a regular triangle. The evaluationresults of the obtained polyester fiber are shown in Table 1.

Example 4

A stretched yarn of polyester fiber of 84 dtex and 14 filaments wasobtained under the same conditions as in Example 2 except that thenumber of discharge holes was 14, a polyester fiber of unstretched yarnof 258 dtex and 14 filaments was obtained, and the obtained unstretchedyarn was stretched at a stretch ratio of 3.07 times. For a triangleobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments in a transverse section of thefiber of the obtained polyester fiber, we confirmed that the ratios ofthe length of each line segment to the average value of the lengths ofthe line segments were 0.97, 1.00, and 1.03, and the figure obtained byconnecting the centroids of the island parts disposed on the outermostperiphery with line segments was a regular triangle. The evaluationresults of the obtained polyester fiber are shown in Table 1.

Example 5

A stretched yarn of polyester fiber of 84 dtex and 72 filaments wasobtained under the same conditions as in Example 3 except that thesea-island ratio was 50:50 in terms of weight ratio. For a triangleobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments in a transverse section of thefiber of the obtained polyester fiber, we confirmed that the ratios ofthe length of each line segment to the average value of the lengths ofthe line segments were 1.00, 0.99, and 1.01, and the figure obtained byconnecting the centroids of the island parts disposed on the outermostperiphery with line segments was a regular triangle. The evaluationresults of the obtained polyester fiber are shown in Table 1.

Example 6

A stretched yarn of polyester fiber of 84 dtex and 36 filaments wasobtained under the same conditions as in Example 1 except that the seapart was changed to polyethylene terephthalate (melt viscosity: 40 Pa·s,melting point: 254° C.). For a triangle obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments in a transverse section of the fiber of the obtainedpolyester fiber, we confirmed that the ratios of the length of each linesegment to the average value of the lengths of the line segments were0.98, 1.03, and 0.99, and the figure obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments was a regular triangle. The evaluation results of theobtained polyester fiber are shown in Table 1.

Example 7

A stretched yarn of polyester fiber of 84 dtex and 72 filaments wasobtained under the same conditions as in Example 3 except that the seapart was changed to polyethylene terephthalate (melt viscosity: 40 Pa·s,melting point: 254° C.), and the sea-island ratio was 50:50 in terms ofweight ratio. For a triangle obtained by connecting the centroids of theisland parts disposed on the outermost periphery with line segments in atransverse section of the fiber of the obtained polyester fiber, weconfirmed that the ratios of the length of each line segment to theaverage value of the lengths of the line segments were 1.03, 1.01, and0.97, and the figure obtained by connecting the centroids of the islandparts disposed on the outermost periphery with line segments was aregular triangle. The evaluation results of the obtained polyester fiberare shown in Table 1.

Example 8

A stretched yarn of polyester fiber of 66 dtex and 96 filaments wasobtained under the same conditions as in Example 3 except that apolyester fiber of unstretched yarn of 115 dtex and 96 filaments wasobtained with discharge holes having a hole diameter of 0.23 mm and thenumber of holes of 96, and the obtained unstretched yarn was stretchedat a stretch ratio of 1.72. For a triangle obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments in a transverse section of the fiber of the obtainedpolyester fiber, we confirmed that the ratios of the length of each linesegment to the average value of the lengths of the line segments were0.99, 1.01, and 0.99, and the figure obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments was a regular triangle. The evaluation results of theobtained polyester fiber are shown in Table 1.

Example 9

A stretched yarn of polyester fiber of 56 dtex and 144 filaments wasobtained under the same conditions as in Example 3 except that apolyester fiber of unstretched yarn of 88 dtex and 144 filaments wasobtained with discharge holes having a hole diameter of 0.20 mm and thenumber of holes of 144, and the obtained unstretched yarn was stretchedat a stretch ratio of 1.57. For a triangle obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments in a transverse section of the fiber of the obtainedpolyester fiber, we confirmed that the ratios of the length of each linesegment to the average value of the lengths of the line segments were0.98, 1.03, and 0.99, and the figure obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments was a regular triangle. The evaluation results of theobtained polyester fiber are shown in Table 2.

Example 10

Polyethylene terephthalate (melt viscosity: 68 Pa·s, melting point: 251°C.) copolymerized with 16 wt % of polyethylene glycol having a numberaverage molecular weight of 8,300 g/mol (PEG6000S manufactured by SanyoChemical Industries, Ltd.) was used as the sea part, and polyethyleneterephthalate (melt viscosity: 120 Pa·s, melting point: 254° C.) wasused as the island part. The polymers for the sea part and the islandpart were separately melted at a spinning temperature of 285° C., andthen weighed such that the sea-island ratio was 90:10 in terms of weightratio. The polymers were allowed to flow into a spinning packincorporating the composite spinneret shown in FIG. 3 , and the inflowpolymers were discharged from discharge holes (hole diameter: 0.30 mm,number of holes: 36 holes) to have a sea-island composite form in whichthe number of island parts disposed on the outermost periphery was 3,and the total number of island parts was 3. The discharged compositepolymer flow was cooled and solidified with a cooling device, suppliedwith a water-containing oil agent from an oil supply device, and thenwound up at a peripheral speed of a take-up roller as a first roller of2,000 m/min, a peripheral speed of a stretching roller as a secondroller of 2,000 m/min, and a winding speed of a winder of 2,000 m/min toobtain a polyester fiber of unstretched yarn of 215 dtex and 36filaments. Subsequently, the obtained unstretched yarn was stretched ata first roller temperature of 90° C., a second roller temperature of130° C., and a stretch ratio represented by a ratio between peripheralspeeds of the first roller and the second roller of 2.48 times to obtaina stretched yarn of polyester fiber of 84 dtex and 36 filaments. For atriangle obtained by connecting the centroids of the island partsdisposed on the outermost periphery with line segments in a transversesection of the fiber of the obtained polyester fiber, we confirmed thatthe ratios of the length of each line segment to the average value ofthe lengths of the line segments were 0.98, 1.02, and 0.99, and thefigure obtained by connecting the centroids of the island parts disposedon the outermost periphery with line segments was a regular triangle.The evaluation results of the obtained polyester fiber are shown inTable 2.

Example 11

Polyethylene terephthalate (melt viscosity: 170 Pa·s, melting point:244° C.) copolymerized with 1.5 mol % of 5-sulfoisophthalic acid sodiumsalt and 1.0 wt % of polyethylene glycol having a number averagemolecular weight of 1,000 g/mol (PEG1000 manufactured by Sanyo ChemicalIndustries, Ltd.) was used as the sea part. Next, a polycaprolactammaster chip was produced by adding 20 wt % of polyvinylpyrrolidone(“Luviskol” K30SP, K value=30, manufactured by BASF SE) topolycaprolactam containing no additives. Subsequently, the master chipwas chip-blended with polycaprolactam (sulfuric acid relative viscosity:2.71, melting point: 220° C.) containing no additives to prepare apolycaprolactam blended polymer having a polyvinylpyrrolidone additiverate of 5.0 wt %, and this blended polymer (melt viscosity: 130 Pa·s,melting point: 220° C.) was used as the island part. A stretched yarn ofpolyester fiber of 84 dtex and 36 filaments was obtained under the sameconditions as in Example 1 except that the polymers were combined as thesea part and the island part, and the sea-island ratio was 50:50 interms of weight ratio. For a triangle obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments in a transverse section of the fiber of the obtainedpolyester fiber, we confirmed that the ratios of the length of each linesegment to the average value of the lengths of the line segments were0.98, 1.02, and 0.99, and the figure obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments was a regular triangle. The evaluation results of theobtained polyester fiber are shown in Table 2.

Example 12

A stretched yarn of polyester fiber of 84 dtex and 36 filaments wasobtained under the same conditions as in Example 2 except that theisland part was changed to “PEBAX MH1657” (melt viscosity: 45 Pa·s,melting point: 203° C.) manufactured by Arkema Inc. For a triangleobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments in a transverse section of thefiber of the obtained polyester fiber, we confirmed that the ratios ofthe length of each line segment to the average value of the lengths ofthe line segments were 1.01, 1.01, and 0.98, and the figure obtained byconnecting the centroids of the island parts disposed on the outermostperiphery with line segments was a regular triangle. The evaluationresults of the obtained polyester fiber are shown in Table 2.

Example 13

A stretched yarn of polyester fiber of 84 dtex and 72 filaments wasobtained under the same conditions as in Example 3 except that thepolymers were allowed to flow into a spinning pack incorporating thecomposite spinneret shown in FIG. 3 , and the inflow polymers weredischarged from discharge holes (hole diameter: 0.30 mm, number ofholes: 72 holes) to have a sea-island composite form in which the numberof island parts disposed on the outermost periphery was 5, and the totalnumber of island parts was 6. For a pentagon obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments in a transverse section of the fiber of the obtainedpolyester fiber, we confirmed that the ratios of the length of each linesegment and to the average value of the lengths of the line segmentswere 1.01, 1.00, 0.98, 0.99, and 1.02, and the figure obtained byconnecting the centroids of the island parts disposed on the outermostperiphery with line segments was a regular pentagon. The evaluationresults of the obtained polyester fiber are shown in Table 2.

Example 14

A stretched yarn of polyester fiber of 84 dtex and 36 filaments wasobtained under the same conditions as in Example 2 except that thepolymers were allowed to flow into a spinning pack incorporating thecomposite spinneret shown in FIG. 3 , and the inflow polymers weredischarged from discharge holes (hole diameter: 0.30 mm, number ofholes: 36 holes) to have a sea-island composite form in which the numberof island parts disposed on the outermost periphery was 9, and the totalnumber of island parts was 12. For a nonagon obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments in a transverse section of the fiber of the obtainedpolyester fiber, we confirmed that the ratios of the length of each linesegment to the average value of the lengths of the line segments were1.03, 1.01, 0.98, 0.99, 1.00, 1.00, 0.98, 0.99, and 1.02, and the figureobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments was a regular nonagon. Theevaluation results of the obtained polyester fiber are shown in Table 2.

Example 15

A stretched yarn of polyester fiber of 84 dtex and 36 filaments wasobtained under the same conditions as in Example 2 except that thesea-island ratio was 65:35 in terms of weight ratio. For a triangleobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments in a transverse section of thefiber of the obtained polyester fiber, we confirmed that the ratios ofthe length of each line segment to the average value of the lengths ofthe line segments were 1.01, 0.98, and 1.01, and the figure obtained byconnecting the centroids of the island parts disposed on the outermostperiphery with line segments was a regular triangle. The evaluationresults of the obtained polyester fiber are shown in Table 2.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Sea part Polymer typePET SIPA-PET SIPA-PET SIPA-PET Melt viscosity (Pa · s) 120 170 170 170Island Polymer type PBT-PEG PBT-PEG PBT-PEG PBT-PEG part Melt viscosity(Pa · s) 50 50 50 50 Spinning Melt viscosity ratio 2.4 3.4 3.4 3.4conditions between sea part and island part Sea-island composite ratio80/20 80/20 80/20 80/20 Stretch ratio 2.38 2.38 1.84 3.07 TransverseFigure formed by centroids Regular Regular Regular Regular section of ofoutermost peripheral triangle triangle triangle triangle fiber islandparts Number of outermost 3 3 3 3 peripheral island parts Total numberof island 3 3 3 3 parts Radius of curvature C of 3.08 2.66 4.29outermost peripheral island part (μm) Circumscribed circle radius 3.793.83 2.83 6.18 L of outermost peripheral island parts (μm) Fiber radiusR (μm) 7.30 7.30 5.19 11.77 Minimum distance S between 0.56 0.62 0.821.00 island parts (μm) Minimum thickness of sea 3.51 3.47 2.36 5.59 part(μm) C/L 0.81 0.69 #VALUE! 0.69 L/R 0.52 0.52 0.55 0.53 S/L 0.15 0.160.29 0.16 Fiber Fineness (dtex) 84 8. 84 84 properties Single fiberfineness 2.3 2.3 1.2 6.0 (dtex) Strength (cN/dtex) 2.6 2.7 2.2 3.1Elongation (%) 43 42 42 43 ΔMR before hot water 4.1 4.2 4.2 3.2treatment (%) ΔMR after hot water 3.7 4.0 4.0 3.1 treatment (%) ΔMRchange with hot water −0.4 −0.2 −0.2 −0.1 treatment (%) EvaluationNumber of breaks of sea 2. 0 1 0 part (piece) Dyeing unevenness 1.3 0.91.1 0.8 Fuzz (piece/m) 2 0 2 0 Drying rate (min) 50 50 45 50 Example 5Example 6 Example 7 Example 8 Sea part Polymer type SIPA-PET PET PETSIPA-PET Melt viscosity (Pa · s) 170 40 40 170 Island Polymer typePBT-PEG PBT-PEG PBT-PEG PBT-PEG part Melt viscosity (Pa · s) 50 50 50 50Spinning Melt viscosity ratio 3.4 0.8 0.8 3.4 conditions between seapart and island part Sea-island composite ratio 50/50 80/20 50/50 80/20Stretch ratio 1.84 2.38 1.84 1.72 Transverse Figure formed by centroidsRegular Regular Regular Regular section of of outermost peripheraltriangle triangle triangle triangle fiber island parts Number ofoutermost 3 3 3 3 peripheral island parts Total number of island 3 3 3 3parts Radius of curvature C of 2.98 3.45 3.70 1.85 outermost peripheralisland part (μm) Circumscribed circle radius 4.11 3.83 4.11 3.60 L ofoutermost peripheral island parts (μm) Fiber radius R (μm) 5.19 7.305.19 3.98 Minimum distance S between 0.82 0.62 0.82 0.63 island parts(μm) Minimum thickness of sea 1.08 3.47 1.08 0.38 part (μm) C/L 0.730.90 0.90 0.51 L/R 0.79 0.52 0.79 0.90 S/L 0.20 0.16 0.20 0.18 FiberFineness (dtex) 84 84 84 66 properties Single fiber fineness 1.2 2.3 1.20.7 (dtex) Strength (cN/dtex) 1.4 2.2 1.3 1.8 Elongation (%) 43 40 42 42ΔMR before hot water 9.5 4.1 9.3 4.0 treatment (%) ΔMR after hot water8.3 3.3 7.3 3.7 treatment (%) ΔMR change with hot water −1.2 −0.8 −2.0−0.3 treatment (%) Evaluation Number of breaks of sea 6 5 8 4 part(piece) Dyeing unevenness 2.4 2.1 3.8 2.3 Fuzz (piece/m) 3 3 7 6 Dryingrate (min) 60 55 60 45 PET: polyethylene terephthalate SPIA-PET:5-sulfoisophthalic acid copolymerized polyethylene terephthalatePET-PEG: polyethylene glycol copolymerized polyethylene terephthalatePBT-PEG: polyethylene glycol copolymerized polybutylene terephthalatePVP: polyvinylpyrrolidone

TABLE 2 Example 9 Example 10 Example 11 Example 12 Sea part Polymer typeSIPA-PET PET-PEG SIPA-PET SIPA-PET Melt viscosity (Pa · s) 170 68 170170 Island Polymer type PBT-PEG PET N6 + PVP PEBAX part Melt viscosity(Pa · s) 50 120 130 45 Spinning Melt viscosity ratio 3.4 0.6 1.3 3.8conditions between sea part and island part Sea-island composite ratio80/20 90/10 50/50 80/20 Stretch ratio 1.57 2.48 2.38 2.38 TransverseFigure formed by centroids Regular Regular Regular Regular section of ofoutermost peripheral triangle triangle triangle triangle fiber islandparts Number of outermost 3 3 3 3 peripheral island parts Total numberof island 3 3 3 3 parts Radius of curvature C of 1.35 2.34 4.13 2.66outermost peripheral island part (μm) Circumscribed circle radius 2.703.71 5.98 3.83 L of outermost peripheral island parts (μm) Fiber radiusR (μm) 3.00 7.30 7.30 7.30 Minimum distance S between 0.47 0.97 0.860.64 island parts (μm) Minimum thickness of sea 0.30 3.59 1.32 3.47 part(μm) C/L 0.50 0.63 0.69 0.69 L/R 0.90 0.51 0.82 0.52 S/L 0.17 0.26 0.140.17 Fiber Fineness (dtex) 56 84 84 84 properties Single fiber fineness0.4 2.3 2.3 2.3 (dtex) Strength (cN/dtex) 1.6 2.9 3.2 2.7 Elongation (%)44 37 44 44 ΔMR before hot water 3.8 3.2 2.2 4.0 treatment (%) ΔMR afterhot water 3.5 2.7 2.0 3.4 treatment (%) ΔMR change with hot water −0.3−0.5 −0.2 −0.6 treatment (%) Evaluation Number of breaks of sea 0 1 2 5part (piece) Dyeing unevenness 0.9 1.2 1.1 2 Fuzz (piece/m) 1 0 0 5Drying rate (min) 40 60 15 55 Example 13 Example 14 Example 15 Sea partPolymer type SIPA-PET SIPA-PET SIPA-PET Melt viscosity (Pa · s) 170 170170 Island Polymer type PBT-PEG PBT-PEG PBT-PEG part Melt viscosity (Pa· s) 50 50 50 Spinning Melt viscosity ratio 3.4 3.4 3.4 conditionsbetween sea part and island part Sea-island composite ratio 80/20 80/2065/35 Stretch ratio 1.84 2.38 2.38 Transverse Figure formed by centroidsRegular Regular Regular section of of outermost peripheral pentagonnonagon triangle fiber island parts Number of outermost 5 9 3 peripheralisland parts Total number of island 6 12 3 parts Radius of curvature Cof 2.04 2.20 3.73 outermost peripheral island part (μm) Circumscribedcircle radius 2.87 3.98 5.08 L of outermost peripheral island parts (μm)Fiber radius R (μm) 5.19 7.30 7.30 Minimum distance S between 0.57 0.430.41 island parts (μm) Minimum thickness of sea 2.32 3.32 2.22 part (μm)C/L 0.71 0.55 0.73 L/R 0.55 0.55 0.70 S/L 0.20 0.11 0.08 Fiber Fineness(dtex) 84 84 84 properties Single fiber fineness 1.2 2.3 2.3 (dtex)Strength (cN/dtex) 2.3 2.7 1.6 Elongation (%) 41 44 41 ΔMR before hotwater 4.1 3.6 6.8 treatment (%) ΔMR after hot water 3.6 3.1 5.7treatment (%) ΔMR change with hot water −0.5 −0.5 −1.1 treatment (%)Evaluation Number of breaks of sea 2 2 5 part (piece) Dyeing unevenness1.4 1.6 1.4 Fuzz (piece/m) 3 2 3 Drying rate (min) 50 50 50 PET:polyethylene terephthalate SPIA-PET: 5-sulfoisophthalic acidcopolymerized polyethylene terephthalate PET-PEG: polyethylene glycolcopolymerized polyethylene terephthalate PBT-PEG: polyethylene glycolcopolymerized polybutylene terephthalate PVP: polyvinylpyrrolidone

Comparative Example 1

Polyethylene terephthalate (melt viscosity: 120 Pa·s, melting point:254° C.) was used as the sea part, and polybutylene terephthalate (meltviscosity: 50 Pa·s, melting point: 217° C.) copolymerized with 50 wt %of polyethylene glycol having a number average molecular weight of 8,300g/mol (PEG6000S manufactured by Sanyo Chemical Industries, Ltd.) wasused as the island part. The polymers for the sea part and the islandpart were separately melted at a spinning temperature of 285° C., andthen weighed such that the sea-island ratio was 80:20 in terms of weightratio. The polymers were allowed to flow into a spinning packincorporating the composite spinneret shown in FIG. 3 , and the inflowpolymers were discharged from discharge holes (hole diameter: 0.30 mm,number of holes: 36 holes) to have a core-sheath composite form in whichthe number of island parts disposed on the outermost periphery was 1,and the total number of islands was 1. The discharged composite polymerflow was cooled and solidified with a cooling device, supplied with awater-containing oil agent from an oil supply device, and then wound upat a peripheral speed of a take-up roller as a first roller of 2,000m/min, a peripheral speed of a stretching roller as a second roller of2,000 m/min, and a winding speed of a winder of 2,000 m/min to obtain apolyester fiber of unstretched yarn of 200 dtex and 36 filaments.Subsequently, the obtained unstretched yarn was stretched at a firstroller temperature of 90° C., a second roller temperature of 130° C.,and a stretch ratio represented by a ratio between peripheral speeds ofthe first roller and the second roller of 2.38 times to obtain astretched yarn of polyester fiber of 84 dtex and 36 filaments. Since thetotal number of island parts was 1 in a transverse section the fiber ofthe obtained polyester fiber, no figure was obtained by connecting thecentroids of island parts disposed on the outermost periphery with linesegments, and thus the obtained polyester fiber had breaking of the seapart at the time of moisture absorption, and dyeing unevenness and fuzzwere generated when the polyester fiber was formed into a fabric. Inaddition, the polymer of the island part was eluted from the broken partof the sea part, and the moisture absorption and release propertiesafter the hot water treatment were also poor. The evaluation results ofthe obtained polyester fiber are shown in Table 3.

Comparative Example 2

A stretched yarn of polyester fiber of 84 dtex and 36 filaments wasobtained under the same conditions as in Example 1 except that the seapart was changed to polyethylene terephthalate (melt viscosity: 500Pa·s, melting point: 254° C.). For a triangle obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments in a transverse section of the fiber of the obtainedpolyester fiber, the ratios of the length of each line segment to theaverage value of the lengths of the line segments were 1.10, 1.04, and0.86, and the figure obtained by connecting the centroids of the islandparts disposed on the outermost periphery with line segments was not aregular triangle. Thus, the obtained polyester fiber had breaking of thesea part at the time of moisture absorption, and dyeing unevenness andfuzz were generated when the polyester fiber was formed into a fabric.In addition, the polymer of the island part was eluted from the brokenpart of the sea part, and the moisture absorption and release propertiesafter the hot water treatment were also poor. The evaluation results ofthe obtained polyester fiber are shown in Table 3.

Comparative Example 3

A stretched yarn of polyester fiber of 84 dtex and 36 filaments wasobtained under the same conditions as in Example 1 except that thesea-island ratio was 40:60 in terms of weight ratio. For a triangleobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments in a transverse section of thefiber of the obtained polyester fiber, the ratios of the length of eachline segment to the average value of the lengths of the line segmentswere 1.09, 0.96, and 0.95, and the figure obtained by connecting thecentroids of the island parts disposed on the outermost periphery withline segments was not a regular triangle. Thus, the obtained polyesterfiber had breaking of the sea part at the time of moisture absorption,and dyeing unevenness and fuzz were generated when the polyester fiberwas formed into a fabric. In addition, since the amount of polyethyleneterephthalate in the sea part was small, the water-absorbing andquick-drying properties were poor. The evaluation results of theobtained polyester fiber are shown in Table 3.

Comparative Example 4

A stretched yarn of polyester fiber of 84 dtex and 10 filaments wasobtained under the same conditions as in Example 2 except that thenumber of discharge holes was 10, a polyester fiber of unstretched yarnof 270 dtex and 10 filaments was obtained, and the obtained unstretchedyarn was stretched at a stretch ratio of 3.21 times. For a triangleobtained by connecting the centroids of the island parts disposed on theoutermost periphery with line segments in a transverse section of thefiber of the obtained polyester fiber, we confirmed that the ratios ofthe length of each line segment to the average value of the lengths ofthe line segments were 0.98, 1.02, and 1.00, and the figure obtained byconnecting the centroids of the island parts disposed on the outermostperiphery with line segments was a regular triangle. However, themoisture absorption and release properties were poor since the sea partwas thick, the fiber had rigidity since the single fiber fineness waslarge, and the texture of the obtained fabric was also poor. Theevaluation results of the obtained polyester fiber are shown in Table 3.

TABLE 3 Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 Sea part Polymer type PET PET PET SIPA-PETMelt viscosity (Pa · s) 120 500 120 170 Island Polymer type PBT-PEGPBT-PEG PBT-PEG PBT-PEG part Melt viscosity (Pa · s) 50 50 50 50Spinning Melt viscosity ratio 2.4 10.0 2.4 3.4 conditions between seapart and island part Sea-island composite ratio 80/20 80/20 40/60 80/20Stretch ratio 2.38 2.38 2.38 3.21 Transverse Figure formed by centroidsN/A Triangle Triangle Regular section of of outermost peripheraltriangle fiber island parts Number of outermost 1 3 3 3 peripheralisland parts Total number of island 1 3 3 3 parts Radius of curvature Cof 3.40 1.53 2.84 6.00 outermost peripheral island part (μm)Circumscribed circle radius 3.40 4.31 6.11 8.65 L of outermostperipheral island parts (μm) Fiber radius R (μm) 7.30 7.30 7.30 16.48Minimum distance S between 0.00 0.30 0.41 1.30 island parts (μm) Minimumthickness of sea 3.90 2.99 1.19 7.83 part (μm) C/L 1.00 0.35 0.46 0.69L/R 0.47 0.59 0.84 0.52 S/L 0.00 0.07 0.07 0.15 Fiber Fineness (dtex) 8484 84 84 properties Single fiber fineness 2.3 2.3 2.3 8.4 (dtex)Strength (cN/dtex) 2.7 1.5 1.1 3.5 Elongation (%) 42 42 43 43 ΔMR beforehot water 4.0 3.8 12.1 1.9 treatment (%) ΔMR after hot water 1.9 1.7 9.31.8 treatment (%) ΔMR change with hot water −2.1 −2.1 −2.8 −0.1treatment (%) Evaluation Number of breaks of sea 15 11 18 1 part (piece)Dyeing unevenness 5.1 6.8 7.3 1.1 Fuzz (piece/m) 16 12 19 0 Drying rate(min) 45 50 70 45 PET: polyethylene terephthalate SPIA-PET:5-sulfoisophthalic acid copolymerized polyethylene terephthalatePBT-PEG: polyethylene glycol copolymerized polybutylene terephthalate

INDUSTRIAL APPLICABILITY

The polyester fiber, in which stress generated with volume swelling ofthe fiber at the time of moisture absorption can be dispersed andbreaking of the fiber surface is reduced, has excellent quality whenformed into a woven or knitted fabric without having dyeing unevenness,fuzz, and the like. In addition, since the hygroscopicity does notdegrade, the fiber has excellent hygroscopicity, and it can be suitablyused particularly in clothing applications.

1-4. (canceled)
 5. A sea-island-type composite fiber comprising anaromatic polyester as a main constituent component of a sea part,wherein the fiber has a moisture absorption/release parameter ΔMR of2.0% or more, and a figure obtained by connecting centroids of islandparts disposed on an outermost periphery in a transverse section of thefiber with line segments is a regular polygon having the centroids asvertexes.
 6. The fiber according to claim 5, wherein a number of theisland parts disposed on the outermost periphery in the transversesection of the fiber is an odd number.
 7. The fiber according to claim5, wherein a ratio C/L of a radius of curvature C (μm) of a side on afiber surface side of an outer periphery of an island part among theisland parts disposed on the outermost periphery in the transversesection of the fiber to a radius L (μm) of a circumscribed circleincluding the island parts disposed on the outermost periphery in thetransverse section of the fiber is 0.50 to 0.90.
 8. A fiber productcomprising the sea-island-type composite fiber according to claim
 5. 9.The fiber according to claim 6, wherein a ratio C/L of a radius ofcurvature C (μm) of a side on a fiber surface side of an outer peripheryof an island part among the island parts disposed on the outermostperiphery in the transverse section of the fiber to a radius L (μm) of acircumscribed circle including the island parts disposed on theoutermost periphery in the transverse section of the fiber is 0.50 to0.90.
 10. A fiber product comprising the sea-island-type composite fiberaccording to claim
 6. 11. A fiber product comprising the sea-island-typecomposite fiber according to claim 7.